Five forms of organizational spontaneity are described (helping co-workers, protecting the organization, making constructive suggestions, developing oneself, and spreading goodwill). Organizational spontaneity is compared with the seemingly analogous constructs of organizational citizenship behavior and prosocial organizational behavior. Based on a selective review of the literature, a multilevel model of spontaneity is presented. Positive mood at work is a pivotal construct in the model and posited as the direct precursor of organizational spontaneity. Primary work-group characteristics, the affective tone of the primary work group, affective disposition, life event history, and contextual characteristics are proposed to have direct or indirect effects, or both, on positive mood at work. Motivational bases of organizational spontaneity also are described. The model and its implications are discussed.